Mike Russell, shadow education minister, will press for the change today (Friday) in a major speech at Moray House School of Education in Edinburgh.
Mr Russell wants to encourage 14 and 15-year-olds to attend FE colleges but stay under the supervision of schools. Several authorities, including East Ayrshire and Fife, have piloted similar initiatives.
"We must not allow rigid structures of schooling to hold in place pupils who would do better elsewhere and whose future may depend on early help to find a vocational route to work," he argues.
But his enthusiasm is not fully endorsed by the Educational Institute of Scotland. Ronnie Smith, the union's general secretary, said that too early a division might damage children's futures. "This is a complex issue but I would not want to see a two-tier system open up. It would bring back memories of the junior and senior secondaries," Mr Smith said.
Pupils could be categorised at the end of S2 into vocational and academic courses, the kind of twin-tracking which had previously been rejected. To channel pupils into low-skilled, manual-type courses could be counter-productive in an increasingly knowledge-based economy.
Mr Russell has no qualms about offering more tailored courses. "Many of the experiments in alternative curricula for the excluded, for school phobics or for disruptive youngsters have been highly successful but I am struck when I visit secondary schools that the difficulty of working in isolation rather than on a national scheme which can offer such chances is very great.
"In addition, pupils who do not present challenges or difficulties to the existing system often do not get the opportunity to have different ways of moving from school to vocational education and training."
Mr Russell adds: "We are in danger of producing a generation of young people who - because they are not interested or attuned to academic subjects - find themselves marking time and wasting time in their final school years."
John Mulgrew, education director in East Ayrshire, said an evaluation of its joint scheme with Kilmarnock College had shown "a very positive effect". Some pupils with difficulties at school found college-based vocational courses much more appealing.
Such initiatives made use of the greater curriculum flexibility granted by the Scottish Executive, Mr Mulgrew said.
Alex Easton, education convener of the Headteachers' Association of Scotland, welcomed the plan, provided parents were consulted and it was carefully thought out. "The principle of flexibility in meeting individual needs is one I would endorse. This may be a more valuable approach for some youngsters," Mr Easton said.